Stringers perform several functions in an aircraft. These functions include transferring bending loads in skin panels, and stiffening the skin panels so the panels don't buckle under loading.
The stringers and skin panels may be made of fiber composites such as carbon fiber reinforced plastic (CFRP). CFRP is being used in place of metal, especially in applications where relatively low weight and high mechanical strength are desirable. CFRP provides a significant improvement in specific strength and stiffness over conventional metal alloys. Better specific strength and stiffness translates into weight savings, which translates into fuel savings and lower operating costs.
A composite stringer is fabricated from multiple plies of reinforcing fibers. Some plies have reinforcing fibers oriented at 0 degrees with respect to the stringer's axis of primary loading. These fibers transfer uniaxial loads. Other plies have reinforcing fibers oriented at ±45 degrees and 90 degrees to transfer shear, transverse and bearing loads. Each ply adds weight to a stringer.
It would be desirable to increase the specific strength and stiffness of composite stringers.